1. Field of the Invention
This invention relates to a transmission or receiving module for an optical link such as optical communications, optical links and optical fiber channels or the like, and more particularly a method for practically loading a small-sized and compact transmission or receiving module for an optical link in which high quality communications can be performed and including rigid flexible board.
2. Description of the Related Art
In recent years, as the technologies of wired or wireless communications such as a cellar telephone, ISDN and the like or processing capabilities in a personal computer or the like have been remarkably improved and also as an audio-visual equipment has been developed for processing signals in digital form, a trend has been promoted in which all kinds of media have been transmitted or received through a network under application of a technology of information communication network.
In a recent trend in which networks such as LAN (Local Area Network) or WAN (Wide Area Network) as well as an internet have been widely distributed for a business use and a personal use, it might be considered to have an environment in the future in which a network is constituted by home-use electric appliances or Audio-Visual equipment within a home mainly on the basis of a personal computer and information processed through a telephone line, CATV, a ground wave TV, satellite broadcastings/communications or the like and in which the elements are freely interactive with each other.
In this case, it is desired to attain a transmission speed such as 100 Mbps to 1 Gbps as a communication capability for making a free interactive operation of image data in a range of several Mbps to several tens Mbps.
At present, although a development of technology about an optical formation mainly on the basis of a main line system for optical communications, LAN or the like, an optical transmission or receiving module used in the above technology is quite expensive. This is caused by the fact that it is necessary to apply a quite precise position alignment technology between a light emitting element and an optical fiber or a light receiving element and an optical fiber in order to keep performances such as transmission speed or transmission quality or the like and that its structure is complex and expensive in view of a countermeasure against a leaked light, an electromagnetic interference or a countermeasure against noise or the like. In order to distribute the optical communications and optical transmission technology for a general purpose, it is an urgent requirement to attain a low cost while its performance is kept at a high level.
In recent years, manufacturing technology to attain a low cost or a high range for POF (Plastic Optical Fiber) such as PMMA (PolyMethyl Meta-Acrilate) or PC (Poly-Carbonate) with its core diameter being large and formed at a low cost has been developed and a problem in positional alignment at a short distance optical transmission with 100 m or less is being eliminated.
FIG. 1 is a side elevational view in section for showing one example of a transmission or receiving module for an optical link for POF and FIG. 2 shows an outer appearance view of it. As indicated in FIGS. 1 and 2, an optical fiber 2 is comprised of a core 2a at its central part and a clad 2b at a circumferential part with a lower refraction rate than that of the core 2a. The extremity end of the clad 2b is provided with a protrusion 2c. The protrusions 2c of the two optical fibers 2 for transmission and receiving are engaged with concave grooves 74a of two holes 74 passed through a fiber installing part 73 of a receptacle module 72, and then the optical fiber 2 is installed at the fiber installing part 73 through its friction lock. A partition plate 75 at the rear end of the receptacle module 72 is provided with each of a light emitting element 77 and a light receiving element 78 in coaxial with the transmission optical fiber 2 and the receiving optical fiber 2. Each of the light emitting element 77 and the light receiving element 78 is stored in a can package, respectively, each of lead terminals 77a and 78a is brought up to a transmission circuit 81 and a receiving circuit 82 on a circuit board 80 having an electric circuit formed thereon and then the lead terminals are directly soldered on the circuit board. ICs 84 are loaded on the transmission circuit 81 and the receiving circuit 82, and a fixing pin 86 for use in fixing the transmission or receiving module 71 for an optical link is fixed to the bottom plate of a casing 85 storing the circuit board 80 therein. Further, wiring pins 87 are connected to the transmission circuit 81 and the receiving circuit 82.
However, in the case of a method for practically loading the transmission or receiving module for an optical link described above, lead terminals 77a, 78a extending from the light emitting element 77 and the light receiving element 78 must be extended over a substantial long distance in the air, resulting in that their lead inductance or the like may become a trouble during a high speed operation and further deterioration in isolation caused by relative inductances at the transmission side and the receiving side may become a problem.
Further, as shown in FIG. 1, it is generally applied that any one of the receiving circuit and the transmission circuit is formed at an upper surface side or a lower surface side in order to avoid interference. However, even if a ground surface is arranged at the central part of the circuit board 80 to divide the upper circuit and the lower circuit into two sections, it may not be avoided to a certain extent that an interference may occur by an electrostatic coupling effect in the ground surface and each of the signal lines. Further, the circuit performing a high speed operation produced a large amount of heat of ICs and the constitution shown in FIG. 1 had a problem that a design for radiating heat became difficult.
In view of the foregoing, it is an object of the present invention to provide a method for practically loading a small-sized and compact transmission or receiving module for an optical link in which an interference between the receiving circuit and the transmission circuit can be prevented, generated heat at the ICs or the like can be radiated efficiently to surrounding atmosphere and also provide a rigid flexible board.
A method for practically loading a transmission or receiving module for an optical link of the present invention is carried out such that at least a pair of optical fibers in the transmission or receiving module for an optical link connected to the optical fibers are installed at a fiber installing part, each of light emitting element and light receiving element is arranged in a direction of optical axis of each of transmission optical fiber and receiving optical fiber installed at the fiber installing part, a first board connected to root portions of the lead terminals of the light emitting element and the light receiving element is integrally formed with a second board and a third board connected to each of both opposing side ends of the first board through a flexible board, and the second board and the third board are bent at a substantial right angle against the first board in such a way that the second board and the third board may be oppositely faced from each other.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that a transmission line having a less amount of deterioration in a signal waveform of which impedance control can be performed is applied on the flexible board.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that each of the second board and the third board is separately formed with each of the transmission circuit and the receiving circuit.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that as the second and the third board as well as the first board, a rigid flexible board having the flexible board connecting each of the boards formed as a core is applied.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that only the flexible board of at least one of the second and third boards is extended be applied as either a power supply or a ground potential and further it is bent and inserted between the second and third boards.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that a metallic partition plate acted as either a power supply or having a ground potential is inserted between the second board and the third board.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that the metallic partition plate inserted between the second board and the third board is integrally formed with at least one of a side surface, a bottom surface and a top surface of a module casing.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that the first, second and third boards are stored in a casing while being bent and a member having a superior thermal conduction is placed between the casing and heat generating components on the second board and the third board.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that further one board or more are connected to each of the second board and the third board through the flexible board.
In addition, the method for practically loading the transmission or receiving module for an optical link of the present invention is carried out such that the flexible board is one or more boards of the first, second and third boards.
The rigid flexible board of the present invention is made such that a first board is integrally formed with a second board and a third board connected to each of both opposing side ends of the first board through a flexible board, this flexible board connecting each of the boards from each other is formed as a core, and the second board and the third board are bent at a substantial right angle against the first board in such a way that the second board and the third board may be oppositely faced from each other, wherein at least one of the second board and the third board has an extended flexible board and this extended flexible board is applied as a power supply or having a ground potential.
In addition, the rigid flexible board of the present invention is made such that a flexible board between the first board and the second board and another flexible board between the first board and the third board are formed with a transmission line having a less amount of deterioration in signal waveform in which an impedance can be controlled.